Few changes in human population history have been more dramatic than the modern decline in fertility in the industrialized world. Since the early nineteenth century, the number of children produced by the average woman over her lifetime has fallen from about six or seven to two or fewer. In the developing world, in contrast, declines in fertility, where they have occurred at all, have generally been more recent and less dramatic. High fertility continues to be a major factor in the persistence of high population growth rates in many parts of the world, contributing to environmental degradation and a wide variety of social and economic problems. From a biomedical perspective, the modern decline in fertility and its differential distribution in time and space pose a number of important questions. For example, given that current reproductive patterns in the industrialized world are recent, historically unique, and in a sense 'unnatural', the physiology of reproduction is unlikely to have evolved to function optimally in its present social and environmental context. What can we learn about human reproductive physiology from baseline data on populations that have not yet undergone the modern fertility decline? For instance, are the rather high levels of fetal loss and widespread pathological sterility observed in industrialized countries typical of the human species as a whole, or are they recent developments? Can improvements in the industrial environment be expected to entail significant changes in reproductive capacity? And have the substantial improvements in nutrition and health that have occurred in Europe and North America over the past century had any measurable impact on fecundity? Conversely, the persistence of high fertility and rapid population growth in certain regions such as sub-Saharan Africa raises questions about the role of fertility in environmental degradation and the likelihood of fertility change in response to such degradation. These issues are central to the emerging field of human reproductive ecology, which combines physiological and demographic approaches to human fertility with perspectives and methods drawn from anthropology, epidemiology, nutritional and environmental sciences, and other cognate disciplines. The proposed conference explores the current state of knowledge in human reproductive ecology. Topical coverage includes the roles of seasonality and nutrition in human fertility, biobehavioral interactions affecting fecundity and fertility, reproductive epidemiology with special reference to pregnancy loss and subfecundity associated with pelvic inflammatory diseases, the design and conduct of empirical research in reproductive ecology, assay standardization and control, and public health implications including current issues in contraceptive research, lactation, and childhood malnutrition. In addition, the conference will address the role played by human reproduction in population growth and environmental change. Speakers will include leading scientists from a variety of disciplines, ranging from diagnostic reproductive endocrinology and biological anthropology through demography, epidemiology, and public health.